I'm not sure by any means, but to me these look like perhaps the same design as the Tak LEs in 5mm, 7.5mm, and 10mm. Anyway, I always assumed these simply clones of the Tak LEs in the shorter focal lengths.

I'm not sure by any means, but to me these look like perhaps the same design as the Tak LEs in 5mm, 7.5mm, and 10mm. Anyway, I always assumed these simply clones of the Tak LEs in the shorter focal lengths.

They can't be the same as the 7.5mm and 5mm Tak LEs because those two Taks are negative-positive designs that get longer (physically) with shorter focal length. My guess, rather, is that these were formerly the Celestron Ultimas of the same focal lengths.

I took one apart 2 or 3 years ago and photographed it because the issue kept coming up. Clyde Crewey sent me his 5mm. It's a doublet Barlow lens (not a Smyth lens) coupled to a doublet-singlet design similar to a 3-element Konig or RKE. I've seen but not disassembled the 7mm Tak LE and presume it to be the same with a different Barlow element. You might be able to find the photo of the 5mm Tak LE in my forum posts on Astromart, if they haven't been destroyed by Herb recently throwing me into the blue-level commercial ATM/OEM sponsor bin. I'll have to cough up $50 for a 10-pack of "vendor" ads just to log in, so I have no idea whether my old forum posts still exist or not. I'd pay the $50 if I actually had a commercial interest of any kind, but I don't, and as it happens, I don't even have anything personal that I want to sell at the moment.

At any rate, search anywhere for photos of the 5mm and 7.5mm Ultimas (was there a 10mm Ultima?) and compare to these Kasai eyepieces.

From telescope to eye, a negative doublet, a 10mm internal field stop, a plano-convex doublet (i.e. plano facing the field end), and a convex-plano (i.e. convex facing the field end) singlet. The eye lens surface seems to be very slightly convex, so the eye lens might be DCX, but that top surface is relatively flat. Appears to be fully multi-coated and the coatings look first rate (very black when looking straight on with a cap on the other end). The upper two elements were spaced by about, 3-4mm or so at the edge (less in the middle, obviously). Didn't measure the height of the spacer. The field stop is not very close to the positive group's field lens surface, and the upper retaining ring is beveled.

Roland mentioned that the design was basically a three element Ortho followed by a Barlow.

Attached Files

Those are Celestron Ultima clones. Unlike the Ultrascopics and Parks Gold Series, the Ultimas got stocky/stubby in the 7.5mm and 5mm focal lengths. I have both a 5mm 7.5mm Ultima. The 7.5mm is bleddy awful. The 5mm is excellent. Both are from the last crop (with the red-orange circle-C logo). Earlier Ultimas featured the lighter orange horizontally bisected circle symbol. I dunno of the prescription changed through time, but my impression is that I've preferred the older units to the newer, with the exception of the 5mm.

Hmm.Astroplan. Very similar to "astroplanokular", the Zeiss-designed 5-element design also called "Super Plossl" by some, and made by Masuyama for years.Since all those eyepieces come/came from Japan and most came from Kasai, I'm betting these are merely the same eyepieces without the familiar brand names:Celestron UltimaOmcon UltimaParks Gold SeriesBaader EudiascopicTuthill Super PlosslsMeade Series 4000 Super PlosslsOrion UltrascopicTakahashi LEand nowKasai Astroplan

The eye relief isn't similar between Kasai astroplan and clone Masuyama. The "Masuyama" clone f=5mm contains 7-lens (Kasai =5lens, without internal barlow).
Nice book about eyepieces is here as follows:http://www.brayebroo...ofEYEPIECES.pdf

When these eyepieces were introduced to the US, the barlow sections in the 3.8mm and 5mm Parks Gold Series/Ultrascopics could be removed.That meant you essentially got two eyepieces in one--a 10/5 couple or a 7.5/3.8 couple.A few years later they started cementing them together so the barlow couldn't be removed from the eyepiece.I had a complete set, and the barlow lens could be inserted in several of the eyepieces, not just the 10 and 7.5.Most of the companies selling these eyepieces didn't have the shorter focal lengths as separate, 5-element, eyepieces because of the extremely short eye reliefs. Adding the internal barlows made the shorter focal lengths with the eye reliefs of the longer eyepieces, which were, in their own rights, already extremely short.